FMS P-51 Build and Mods

I bought this Version 2(they're now upto V5 with servoless retracts and upgraded elevator servo standard now) FMS P-51 Mustang 1.46m EPO foam warbird from AerialHobby in Singapore and it was the kit only as I wanted to build it up and learn in the process. I have followed and used some of the mods on the RCgroups thread about this plane as well as implemented some of my own. Below is a list of the the mods which I have done so far along with the materials I've used and setup I'm running. Most of the internals were bought from HK which I think proves it doesn't have to cost you a packet to get a nice bird like this built Not all the mods below are necessary for this plane to fly as alot of guys are running it stock however if you have a ARF or RTF I'd strongly recommend atleast using a metal gear servo for elevator and running a separate BEC if you don't already.
Am going to run it with the stock four blade prop that comes with the plane and see how I go.

The ESC and seperate BEC are probably bigger than is needed but hey...why not The modifications I have done so far are below and have some pics and video also. The pics for the rear retract are not taken from my mod but I used the same basic principle as the one photographed along with the shortened tailwheel.

So far I have:

Installed retracts
Installed a Turnigy 3 Channel Servo Speed/Direction Regulator to reverse one servo and slow down the retracts and make them look more scale during operation(can do)
Shortened the tailwheel to help it sit lower(can do)
Made the tailwheel retractable and steerable(can do)
Installed flaps along the original line where it should be(can do)
Increased forward rake on the main gear to help against nose overs(should do)
Re-inforced the main gear to spread load on landings(should do pre V5)
Weathered gun trails on the wings
Painted the pilot
Put both UHF and VHF scale looking antennas
Added another 6mm square CF rod into the servo wire wing channel for added strength(can do)
Installed 2 working bomb modules on wings
Installed separate BEC 5-7.5amp (below is a pic showing how to wire one into your power system)

on a rhino 3700 3s 25c the results were almost identical apart from a 3W gain in power

where this motor starts to show it's true colours I thought is on 4s and above, test was using a Rhino 3700 4s 25c and an APC 14x10E 2blade prop WOT and I left the spinner off and was at 15seconds.

60.89A (64.68A initial peak)
14.74V
897.5W
7580rpm

I also used a Turnigy 3600 4s 30C and the stock 4blade and got the following but *NOTE* THE BELOW FIGURES ARE STATIC 'PEAK' AND NOT AT 15 SECONDS AS WITH THE 2BLADE. Take off approx 6-8% to get figures at 15seconds.

63.40A
15.37V
and ....987WATTS!!! @ 6450rpm
I thought it was maybe a little high so did it again and on the 2nd run got
67.50A
15.32V
and 1034Watts!....forgot to record the rpm 2nd time round
looks like this plane is gonna be black and white depending on which battery I end up flying with

***UPDATE 25/4/2010***This seems to be a work in progress but after putting a few flights through her the following has happened.
-I have since changed to a 5S power system using 4000mAh batteries (the results are in the pic/table and were obtained using the eagletree inflight logger)to reduce the amp draw, maintain performance and increase flight times which are now around 8-10mins with 1KW power.
-I have had to re-hinge the elevator and rudder with plastic/nylon hinges due to the foam coming away.
-I have also replaced the tailwheel arm that holds the wheel to the retract as the stock was too soft and bent/broke so I fabricated another out of thicker aluminium and has so far worked well
-Also replaced the 14g mg retract servo(broke after thick grass got caught in my tailwheel assembly and caused it to bind ) to a larger 17g mg the same as the main gear and relocated it next to the elevator and rudder servo with a longer pushrod for easier maintenance.(see pic)
-One of the main gear retracts has broken and have had to replace. Will also install some VQ offset .40 size sprung struts to help cushion landings.
-Made some collars to fit onto the retracts to help strengthen them(see attached pics).
-I've also noted the plastic from which the bombs are made out of is of poor quality and breaks too easily when they hit the deck(grass). Will fabricate/experiment with some foam ones and see how they go and report back.
-Changed the way in which I supported the retracts to the wing, I now use two wooden strips, shaped and then epoxied into the wing. They have so far proven to work well and saved me about 100gms weight from my previous method.

I can say that this plane flies SOOOOO SWEET and even with the extra weight she still handles beautifully and the flaps work very well to slow her down for landings. I highly recommend this plane and even for someone who isn't confident in doing any mods she flies great straight out the box...just invest in a separate UBEC and a decent metal gear elevator servo and you should be fine....HAPPY FLYING!

John

***UPDATE 15/5/2010*** I have recently upgraded the stock retracts and installed new DSR version 2 TITAN(stronger than standard DSR's) servoless retracts along with VQ struts and they've so far stood up ok. This is a possible upgrade for anyone looking to switch over from mechanical to electric retracts. They are a little expensive and now I believe you can buy replacement FMS electric retracts which are cheaper and seem to be ok.

*** UPDATE 1/2011*** I had to remove the Turnigy SK 5055 580kv motor for another plane and have again gone back to the Turnigy SK4250 650kv motor and run it on 4S with 2x2200 batteries in parallel and a 13x10 sport prop. Performance has obviously dropped but it's still quite quick and has more power than is necessary. Plus side is that I have saved about 150g in weight with the motor and battery changes.

Here is a video that shows the bombs in action, there's also a bit of history for all the mustang fans out there

Yeah the motor's going strong no complaints. If you're not too concerned about the extra weight that this motor and a 5S battery brings, then I say go for it. It's probably overkill for this size/weight foamie as alot of the guys on the thread have proven already it flies great with a smaller motor/4S system.
At the end of the day I think this motor(50-55) is more suited to 5S or 6S, the plane flew great on 4S I just wanted to bring the amps down for longer flights so went 5S with a smaller prop. I do have a 14x10 APC prop but I'm currently getting around 1KW of power with the 12x6, so putting a 14x10 might jump the amp draw up a lil high for my liking and would turn it into a helicopter me thinks ..it already has unlimited vertical even with all the extra weight I have on it
The only thing I would suggest is if you do get any Turnigy SK motor, check and even remove and put some loctite on where the end cap screws onto the bell as mine came loose after a few flights. I did mention this on the thread a few months back and posted some pics which you probably wouldv'e seen but apart from that, all good in the hood plenty of power, low ish amp draw, motor comes down luke warm and she can run 3S(yep I've done it ) upto according to HK 8S which is way more than I'll ever need.

Thanks Basil, I'm not exactly sure which pieces you're referring to? I bought the kit and I simply just left the servo connector with the servo in it's little holder when I built mine so when I changed over to DSR's I just unplugged the old servo and installed the new DSR. I couldn't see why you couldn't use a hobby knife and just carefully cut along the glue where the little foam covers for the servo wire channel is...